Rotary blade unmanned aerial vehicles (UAVs) are often designed to carry a payload and/or to remain airborne for a specified duration of time. For example, a UAV such as a helicopter, a quad-copter, or an octo-copter may be designed to carry a payload of up to 10 pounds and remain airborne for up to 30 minutes. To carry a larger payload, the UAV typically has to be larger, with larger motors, larger propellers, more propellers, and/or larger power modules to generate the lifting force sufficient to carry the larger payload. Likewise, for extended flight duration, additional or larger power modules are often used.